This project is directed at understanding the native molecular speciation of high density lipoproteins, the functional roles of individual HDL species, and the processes by which they are generated and catabolized. It also includes study of the influence of mutations and polymorphisms in key genes involved in HDL metabolism with the objective of identifying genomic determinants of HDL speciation and the genetic basis of HDL deficiency disorders. Specific Aims: 1) To complete the isolation and characterization of the native molecular species of human HDL using selected affinity immunosorption. The stoichiometry of constituent proteins and lipids in those species will be established by immunochemical methods and mass spectroscopic analysis. 2) To continue to isolate novel proteins from human HDL and elucidate their gene structures. Candidates are proteins discovered by mass spectroscopic analysis that are not present in sequence databases. 3) To characterize the HDL species that are substrates and products of SR-Bl, -hepatic lipase (HL), -phospholipid transfer protein (PLTP), and - mediated reactions. 4) To develop methods for quantitative measurement of individual HDL species in plasma. 5) To study the composition and distribution of plasma HDL species of HDL deficient subjects. 6) To determine the impact of mutations andpolymorphisms in the HL, PLTP, SR-BI, the ABCA1 transporter, and apolipoprotein L genes on the metabolism of individual molecular species of HDL.